1. Field of the Invention
The present invention relates to a photographing control technique which simultaneously uses a mechanical shutter and an electronic shutter.
2. Description of the Related Art
A single-lens reflex digital camera incorporates a mechanical focal plane shutter (to be referred to as a mechanical shutter hereinafter) having a first curtain and a second curtain, and limits the exposure time by movement of the first curtain and second curtain in normal photography. There is also proposed a camera which performs an image sensing operation by simultaneously using a mechanical shutter and an electronic shutter. The mechanism which simultaneously uses a mechanical shutter and an electronic shutter uses the mechanical shutter for the second curtain, and takes a photograph by electric charge accumulation by starting scanning of the pixels of an image sensing element prior to travel of the second curtain.
An image sensing element using a CMOS sensor performs pixel reset (scanning for resetting the accumulated electric charge amount of a pixel to zero) for each pixel or each image sensing region including a plurality of pixels. After a predetermined time has elapsed, signal readout scanning is performed for each pixel or each region, thus implementing an electronic shutter. That is, in such electric charge accumulation of an image sensing element, for each scanning line pixels are reset and electric charge accumulation is started (such electric charge accumulation start scanning will be referred to as reset scanning hereinafter). After that, the second curtain of a mechanical shutter shields the image sensing element against light, and scanning for reading out the electric charges accumulated in the respective pixel elements is performed. Therefore, the pattern of this reset scanning is matched with the traveling characteristic of the mechanical shutter for the second curtain (e.g., Japanese Patent Laid-Open No. 11-41523 (paragraph Nos. 0044 to 0050, FIGS. 1 to 3 and the like)).
A general single-lens reflex digital camera uses an exchangeable photographing lens, and can therefore change the focal length and the exit pupil distance (the distance from the image sensing plane to the lens pupil position). Assume that a mechanical shutter and electronic shutter are simultaneously used. The electronic shutter is activated on the image sensing plane, while the mechanical shutter is spaced apart from the image sensing plane in the optical axis direction. For this reason, the light-shielding position, on the image sensing plane, of the mechanical shutter changes depending on, for example, the focal length and exit pupil distance. Particularly when the time from reset scanning until light shielding by the mechanical shutter is relatively short, unevenness of exposure occurs in the shutter scanning direction depending on the conditions of the photographing lens.
Examples of the conditions of the photographing lens are the presence/absence of pupil position information, whether the lens is a shift lens, the shift amounts of a shift lens and antivibration lens, whether the lens has an accessory adapter for changing the pupil position, and whether an extension tube is attached to the lens. Since the light-shielding position, on the image sensing plane, of the second curtain of the mechanical shutter changes depending on these factors, unevenness of exposure occurs in the shutter scanning direction as described above.